i had the same noise on my 00-500 sc. i'm now the proud owner of a complete new rearend. better make sure your bearing hub is FULL of grease.

 

I hate to say anything else because the list of could bes is getting bigger but I had a clancking sound coming from below my floorboards so I took off my pvt cover and reved my scrambler in Neutral a couple of times and let off and the sound came from the front primary clutch. The six little spyder buttons/ramp buttons in the front worn out and one or two fell out completly. That was my noise. They were easy to replace but you need to have a special spyder removal tool to be able to put the buttons in. Since it was apart I took the rear secondary clutch off and pulled it apart and noticed that I needed to replace the three ramp buttons in the rear. One of the torx screws that holds the buttons in place was broke off so I just ordered a roller clutch from AAEN to get rid of the buttons all together. You MUST check these wear items in the clutch area every six months to a year depending on how much and how hard you ride, they DO wear out!

Later,

 

I also think that it is your belt slapping on your pvt cover.

 

I also think that it is your belt slapping on your pvt cover.